Chemistry of haloalkanes

• Haloalkanes are polar due to the carbon-halogen bond in the structure. Halogen atoms are more electronegative than carbon atoms, so the electron pair in the carbon-halogen bond is therefore closer to the halogen atom than the carbon atom.
• The slightly positive charge on the carbon atom can attract it species containing a lone pair of electrons. This species donates a pair of electrons to form a new bond.
• Species that donate a loan part of electrons are known as nucleophiles. A nucleophile is an atom or group of atoms that is attracted to an electron-deficient carbon atom, where a donates the pair of electrons to form a new covalent bond.
• When a haloalkane reacts with a nucleophile, the nucleophile replaces the halogen in a substitution reaction. The reaction mechanism is nucleophilic substitution.
• Hydrolysis is a chemical reaction involving water on an aqueous solution of hydroxide that causes the breaking of a bond in a molecule.
• In the hydrolysis of a haloalkane, the halogen atom is replaced by an -OH group. This is an example of a nucleophilic substitution reaction, which takes place as follows:

  1. The nucleophile approaches the carbon atom attached to the halogen on the opposite side of the molecule from the halogen atom
  2. This direction of attack by the other ion minimizes propulsion between the nucleophile and the 𝛿- halogen atom
  3. A lone pair of electrons on the hydroxide ion is attracted and donated to the 𝛿+ carbon atom
  4. A new bond is formed between the oxygen atom of the hydroxide and the carbon atom
  5. The carbon-halogen bond breaks by heterolytic fission
  6. The new organic product is an alcohol. A halide ion is also formed.
• Haloalkanes can be converted to alcohols using aqueous NaOH or KOH and heated under reflux.
• The rate of hydrolysis increases as the strength of the carbon-halogen bond decreases:

  • Iodoalkanes react faster than bromoalkanes
  • Bromoalkanes react faster than chloroalkanes
  • Fluoroalkanes are unreactive as a large quantity of energy is required to break the C-F bond
• To measure the rate of hydrolysis of haloalkanes with water, you can carry out the reaction in the presence of aqueous silver nitrate. As the reaction takes place, the halide ions are produced, which react with the silver ions to form a precipitate of their silver halide. The reaction is carried out in the presence of an ethanol solvent, which allows water and the haloalkane to mix and produce a single solution.